Nanoparticle production by UV irradiation of combustion generated soot particles

Abstract

Laser ablation of surfaces normally produce high temperature plasmas that are difficult to control. By irradiating small particles in the gas phase, we can better control the size and concentration of the resulting particles when different materials are photofragmented. Here, we irradiate soot with 193 nm light from an ArF excimer laser. Irradiating the original agglomerated particles at fluences ranging from 0.07 to 0.26 J/cm 2 with repetition rates of 20 and 100 Hz produces a large number of small, unagglomerated particles, and a smaller number of spherical agglomerated particles. Mean particle diameters from 20 to 50 nm are produced from soot originally having a mean electric mobility diameter of 265nm. We use a non-dimensional parameter, called the photon/atom ratio (PAR), to aid in understanding the photofragmentation process. This parameter is the ratio of the number of photons striking the soot particles to the number of the carbon atoms contained in the soot particles, and is a better metric than the laser fluence for analyzing laser-particle interactions. These results suggest that UV photofragmentation can be effective in controlling particle size and morphology, and can be a useful diagnostic for studying elements of the laser ablation process.2

Photochemical Interaction of Polystyrene Nanospheres with 193 nm Pulsed Laser Light

“…When these results are compared with our previous results of soot 20 and NaCl 19 particles irradiated at 193 nm, similarities and differences are observed. The nonirradiated soot and NaCl particles have agglomerated structures composed of ∼40 nm spherical primary particles with a fractal dimension (D f ) of approximately 1.8 and log-normal size distributions with mean diameters of 265 and 120 nm, respectively.…”

“…While we observed atomic and molecular fluorescence using 193 nm light, neither incandescence nor plasma formation was seen from the different particles (polystyrene, soot, and NaCl). [18][19][20][21] However, when we replaced the 193 nm laser with a frequency-doubled Nd:YAG laser at 532 nm, long lifetime broadband incandescence was observed from the same particles at similar fluences. Unlike nanosecond laser irradiation at longer wavelengths, thermal effects are negligible in 193 nm laser photochemistry of polymer surfaces, and the thermal effects increase with the incident wavelength.…”

“…[17][18][19][20][21] Photochemical bond breaking through electronic excitation is the dominant mechanism rather than thermal desorption. Some of the species liberated by photofragmentation are subsequently electronically excited and fluoresce, which can be measured as a signature of the particles.…”

“…The results are used to analyze the interactions of polydisperse, agglomerated soot and NaCl particles with 193 nm light from our previous studies. 19,20 Ultimately, this work will provide some insight into physical processes in particle disintegration and production by a UV laser. Figure 1 shows the experimental apparatus of particle generation and measurement system.…”

Soot Measurements in Steady and Pulsed Ethylene/Air Diffusion Flames Using Laser-Induced Incandescence

“…This provided efficient mixing and improved the combustion regime. Stipe et al (2004) suggested that UV photo fragmentation can be effective in controlling particle size and morphology, and can be a useful diagnostic for studying elements of the laser ablation process. propane, and benzene).…”